Introduction/Background: Acid-BaseExtraction is one of the most useful separation techniques in organicchemistry. This separation is composed of a solvent-solvent extraction.”Extraction results from the unequal distribution of solute between twoimmiscible solvents.” (Solomon, 2010) The purpose of this type of extractionfalls in the usage of the acid-base properties in organic compounds and theisolation of the same when they are present in a mixture. A separation of amixture of an acid, a base, and a neutral compound is formed; these mixturesthen separate into their individual components.
The theory behind this type ofextraction lies in the addition of either an acid or a base to a mixture sothat it separates its components; it also acts in the recrystallization of thesame in order to be purified and isolated (Nguyen, 2013). Theaim of this experiment is to separate a mixture of benzoic acid (Figure 1),4-chloroaniline (Figure 2) and naphthalene (Figure 3), and figure out thepurity of the mixture using their melting point range. The acid-base reactionused in this experiment consists of adding either an acidic or basic solutionto an acidic mixture depending on what the desired result is. If one wants toturn the solution more basic, an acid is added; if one wants a more acidicsolution, then a basic solution is added into the mixture.
ExperimentalSection: 1) Weightout 1:1 ratio of 3g of starting solutes2) Dissolvein diethyl ether (30-mL) and put it in 125-mL separatory funnel using 20-mLfresh ether3) Add30-mL of 5% HCl, close the separatory funnel and shake to mix4) Ventthe separatory funnel and close and shake again5) Repeatuntil fully mixed6) Allow2 phases to separate into layers7) Drawout the lower layer into Flask #18) Add3M NaOH to generate amine in Flask #19) Dryusing a vacuum then weight the residue10) Add 50-mL of 5% NaOH toseparatory funnel 11) Shake until fully mixed (asdone before)12) Draw off the lower layer intoa Flask and label it Flask #213) Add 6M HCl to Flask #2 whilethe flask sits in an ice bath14) Remove, dry, and weight asdone before15) Add 20-mL of NaCl solution toseparatory funnel and drain bottom layer16) Label the flask: Flask #317) Dry and weight as done before18) Take each product’s meltingpoint using a melting point apparatus to determine the purity of each solution19) Record all of the residues’weight and their melting points Table ofChemicals: Physical Properties Benzoic Acid 4-chloroaniline Naphthalene Molar mass 122.12 g/mol 127.57 g/mol 128.17 g/mol Melting point 122 °C 68.0-71.
0 °C 80.0 °C Vapor pressure 10.0 mmHg (132 °C) 0.15 mmHg (25 °C) 0.03 mmHg (25 °C) Boiling point 249.2 °C 232.0 °C 218 °C Appearance Colorless crystalline solid Pale yellow solid White solid crystals/flakes, strong odor of coal tar Density 1.
27 g/mL 1.43 g/mL 1.14 g/mL Chemical Properties Benzoic Acid 4-chloroaniline Naphthalene Solubility in water 2.90 g/L 2.60 g/L 30.0 mg/L Flammability Flammable Flammable Highly flammable Reactivity Incompatible with strong bases, strong oxidizing agents, alkalies. Incompatible with strong oxidizing agents, acids, acid chlorides, acid anhydrides, chloroformates, nitrous acid. Can react exothermically with bases.
Enthalpy of formation ?386 kJ/mol ?33.3 kJ/mol ?5.16×103 kJ/mol Acidity pKa: 4.2 pKb: 10 NA Heat of combustion 3229.0 kJ/mol ?7669.
0 kJ/mol ?5288.6 kJ/mol Table #1:Physical and Chemical Properties of the compounds used in the experiment. Results: Mixtures Mass Percent Recovery Melting Points: Benzoic Acid 1.015g 101.5% 94°C 4-Chloroaniline 0.947g 94.
7% 78.3°C Naphthalene 0.499g 49.9% 85°C Table #2: Mass,percent recovery, and melting point of all the compounds used.PercentRecovery CalculationsBenzoic Acid:4-Chloroaniline:Naphthalene: Discussion: The results for the experiment are shownin Table #2. The table shows the mass calculated for each individual compound,along with their measured melting points and calculated the percent recoveries.
The percent recovery was calculated using the mass recovered versus the amountthat was actually supposed to result in the experiment. Basically the amountrecovered is divided by the amount expected in the procedure then the value ismultiplied by 100 so that we have a percent value. The percent recovery valueaids in the determination of the purity of an isolated compound. According to the results obtained, thehighest percent recovered was that of benzoic acid, 101.
5%. It was the highest percentout of the three substances. This result shows that there was 1.5% of impurity whenextracting the benzoic acid.
This may be because the solution contained morethan what was supposed to be in the mixture. The other percent recoveriesranged below the 100%. 4-chloroaniline was calculated to be 94.7% andnaphthalene resulted in ~50%. The percent recoveries are below 100%because, since the beginning of the experiment, the mixture may not be 1:1:1ratio due to impurities. Also, another possible reason could have been humanerror. There could have been a mistake in the transferring of the solution tothe butcher funnel.
There could have been left over solution in the flask usedto collect the solution. Another human error could possibly be an error in measurementof the substances. All these factors could alter the values obtained for thepercent recoveries for all the compounds. Measuring the melting points of thecompounds is another way to determine their purity.
To determine each isolatedcompounds’ melting points, a melting point apparatus was used. Using the apparatus one could see that all ofthe melting point values were lower than the literal values provided. There arevarious ways as to why the values differed: a rapid increase in the temperatureinside the apparatus, or the compounds extracted could have had impurities whencollected. An impurity is known to alter the results obtained in an experiment.Conclusion The main purpose of this experiment wasto separate amixture of benzoic acid, 4-chloroaniline and naphthalene, and figure out thepurity of the mixture using their melting point range. Inthis experiment the acid-base extraction of an organic acid, base and neutralwas performed successfully. Even though there may have been human errors in thecalculations, the overall procedure work relatively well.
In an experiment ofthis sort, the chemical compounds of the mixtures can help understand thedifferent reactions that could occur when the same solutions are mixed withother substances. These chemical properties can also be used to makeextractions of certain isolated compounds. They help determine what substancecan be used to separate the mixtures.
Thus, in this experiment one could seeclearly the interaction of an acid with a base and how the desired productdissolves in one of the solvents, which are immiscible (Solomon, 2010). Thepercent recovery and melting point calculated in this experiment were used toverify the purity of the extracted compounds. Acid-base reactions can be, notonly used for the separation of organic compounds, but also in the removal ofimpurities from different compounds.
This laboratory accomplished what set outto do because the extractions were performed successfully and clearly using allof the concepts related to acid-base extractions. References:L. (2013, December18). Acid-Base Extraction. Retrieved January 29, 2018, from https://chem.
libretexts.org/Demonstrations_and_Experiments/Basic_Lab_Techniques/Acid-Base_ExtractionNguyen, V. Prezi. http://prezi.
com/–uku_uckcxy/acid-base-extraction/ (accessed January 2018).Solomons,Thomas W. Graham, and Craig B.
Fryhle.Organic Chemistry. 7th ed. Hoboken,N.
J.:Wiley, 2010. Print.